The study of chemical damage to DNA by ionizing radiation has centered largely on strand breaks. The study of base damage has been limited due to the lack of sensitive and specific assays capable of measuring specific products at low, biologically significant doses. Serological assays such as radioimmunoassays are extremely sensitive and specific. We have developed such assays for several damaged bases, among them thymine glycol and 8-hydroxyadenine, and are using them to study the production and repair of damaged bases in irradiated DNA of cellular systems.